Reading skills - SANDS OF TIME

     Sand: as children we play on it and as adults we relax on it. It is something we complain about when it gets in our eyes on a windy beach, and praise when it is made into sand castles. But we don't often look at it. If we did, we could discover an account of a geological past and a history of sea life that goes back thousands and, in some cases millions of years.

     Sand covers not just seashores, but also ocean beds, deserts and mountains. It is one of the most common substances in the world. And it is a major element in manufactured products too - concrete* is largely sand, glass is made of little else.

     What exactly is sand? Well, it is larger than fine dust and smaller than shingle*. In fact, according to the most generally accepted scheme of measurement, grains can be called sand if their diameter is greater than 0.06 of a millimetre and less than 0.6 of a millimetre.

     Depending on its age and origin, a particular sand can consist of tiny stones or porous grains through which water can pass. These may have the shape of stars or spirals, their edges rough. They have come from the breaking down of rocks, or from the dead bodies of sea creatures, which collect on the bottom of the oceans, or even from volcanic eruptions.

     Colour is another clue to the origins of sand. If it is dazzling white, its grains may come from nearby coral, from crystalline quartz rocks or from gypsum, like the white sand of New Mexico. On Pacific Islands, jet black sands form from volcanic minerals. Other black beaches are magnetic and are mined for iron ore.

     Rain is an important force in the creation of beaches. It washes rock into streams and rivers and down to the sea, leaving behind softer materials. By the time it reaches the sea, the hardest rocks remain but everything else has been broken into tiny particles of 0.02 millimetre diameter or less. The largest pieces fall to the bottom quickly, while smaller particles float ans settle only slowly in deeper water, which is why the sandy beaches on the shoreline so often turn to mud further out.

     It can be difficult to date the sand on the beach accurately but it is possible to get a general idea of whether or not the sand is 'young' or 'old'. If the individual fragments still have sharp edges, you can be sure they were formed fairly recently. This is the case in the island of Kamonoama in Hawaii, where a beach was created after a volcanic eruption in 1990. Molten lava spilled into the sea and exploded into glassy droplets.

     It seems that when the poet William Blake saw infinity in a grain of sand he was not far wrong. Sand is an irreplaceable industrial ingredient which has many uses. In addition it has one vital function which you might never even notice. Sand cushions our land from the force of the sea, and geologists say it often does a better job protecting our shores than the most advanced coastal technology.
 

concrete - building material (betonas); shingle - small rough pieces of stone in the shore by a sea or a river
 

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